Circuit breaker with thermal release and compensation for ambient temperature and contact-resistance heating



Oct. 5, 1965 A. R. NORDEN 3,210,500

CIRCUIT BREAKER WITH THERMAL RELEASE AND COMPENSATION FOR AMBIENT TEMPERATURE AND CONTACT-RESISTANCE HEATING- Filed Aug. 1, 1962 INVENTOR. fllexarzdkr R. 4 0/27? BY @J W United States Patent CIRCUIT BREAKER WITH THERMAL RELEASE AND COMPENSATION FOR AMBIENT TEM- PERATURE AND CONTACT-RESISTANCE HEATING Alexander R. Norden, New York, N.Y., assignor to Federal Pacific Electric Company, a corporation of Delaware Filed Aug. 1, 1962, Ser. No. 213,988 8 Claims. (Cl. 200116) The present invention relates to circuit breakers and has particular application to automatic circuit breakers of the type in which the mechanism is supported and onclosed between two pieces of molded insulation.

An object of this invention resides in providing improvements in a well-known type of circuit breaker mechanism of the type having a pivoted contact arm carried by a fixed pivot, in which the contact-carrying arm carries an overload release latch and a normally latched pivoted actuator, with a view toward decreasing nuisance tripping.

Another object of the invention resides in the provision of an improved ambient temperature compensating mechanism for cooperation with an overcurrent latch in a circuit breaker mechanism.

Still another object of the invention is to provide a circuit breaker having integrated therein a current responsive tripping device having means for compensating for the heating produced at the breaker contacts.

Two embodiments of the invention are described in greater detail below. In both embodiments a circuit breaker is provided having circuit making and breaking contacts and a so-called split case of molded insulation. A movable contact element is pivotally supported by the contact carrier which, in turn, is pivoted between the halves of the casing. A bimetallic overcurrent responsive latch is secured at one end to the pivoted contact element and its other end cooperates with an actuator that is pivoted on the contact carrier. A trippingpoint compensator cooperates with the contact carrier and with the pivoted contact element to adjust the position of the overcurrent latch relative to the actuator.

In one embodiment, the compensator adjusts the tripping point to compensate for ambient temperature only. In the other embodiment the compensator is in good heattransfer relationship to the junction of the current responsive bimetal and the movable contact and in this embodiment the compensator is effective to compensate for a certain amount of down-rating of the main bimetal that results from local heating at the contacts and to compensate for ambient temperature changes.

The nature of the invention and its further features of novelty will appear from the following detailed disclosure of the embodiments of the invention shown in the accompanying drawings.

In the drawings:

FIG. 1 is a side elevation of an illustrative embodiment of the invention with one side wall of the casing removed to reveal the internal mechanism;

FIG. 2 is an enlarged view of a portion of the circuit breaker in FIG. 1, partly in cross-section, with the contacts closed;

FIG. 3 is a fragmentary cross-section of part of the mechanism in FIG. 2, further enlarged, as viewed from the plane 33 of FIG. 2;

FIG. 4 is an enlarged fragmentary cross-section of part of the circuit breaker in FIG. 1 as viewed from the plane 44 in FIG. 1;

FIG. 5 is a greatly enlarged fragmentary top view partly in section, of another part of the circuit breaker of FIG. 1 as viewed from the plane 55 in FIG. 1; and

FIG. 6 is a fragmentary enlarged view, similar to FIG. 2, of a portion of another embodiment of the invention.

Referring now to FIGS. 1 through 5, the circuit breaker shown therein has an enclosure 10 comprising front and rear casing walls 12 and 14 respectively, made of molded insulation. A pair of terminals 16 and 18 are mounted at opposite ends of the enclosure 10. A moving contact carrier 20 is supported between its ends on a pivot spring 22. The pivot spring 22 cooperates with bearing portions formed in the casing walls (FIG. 4). An operating handle 24 having a lever portion 26 protruding from an aperture 28 in the enclosure 10 is supported on pivots 30 which have bearings (not shown) in the casing walls 12, 14. The handle 24 is connected to the bell crank or actuator 32, pivoted on the arm 20, by the rigid U- shaped wire link 34. The pivoted actuator 32 has an insulated bearing (not shown) at the right-hand end of the contact carrier 20. Spring 36 reacts between the contact carrier 20 and a portion of the handle 24, and provides contact-opening bias as well as bias for returning the handle 24 to the off or open circuit indicating position shown in FIG. 1. This bias against the carrier 20 and the handle 24 is applied in both the open and closed positions of the breaker mechanism. The spring bias urges both members toward their off or open circuit position.

A stepped (multiple-diameter) rivet 38 is secured, as by peen 38a, to a depending portion 40 of the contact carrier 20. The rivet body supports a contact element 42 of copper having a contact 44 of sintered silvertungsten. The contact element is pivotal on the rivet 38 between the head 38b and the carrier portion 40. Contact 44 cooperates with a companion sintered silvertungsten contact 46 carried by the wire-connecting terminal 16. Contacts 44 and 46 cooperate in a region of the casing which forms an arc chamber and has a vent 48 to the exterior.

Referring to FIG. 2 a current-responsive bimetal 50 is joined by a rivet 52 (which extends integrally from element 42) to the contact element 42. A tripping-point compensator 54 of bimetal is joined to the element 42 by a rivet 56 (which also extends integrally from element 42) adjacent the pivot 38, so that the tripping point compensator '54, the contact element 42, and the currentresponsive bimetal 50 form an integral unit pivotally supported by contact carrier 20.

The free end of bimetal 50, remote from the pivot 38, engages a finger 51 which depends from the actuator 32. A stop 58 projects from the rear casing wall so as to underlie the main bimetal 50.

Another depending portion 60 of the contact arm carries a coil 62 of flexible copper braid joined to bimetal 50 near the right hand extremity of the bimetal, the braid having an extension 64 that is united to plug-in terminal 18 of the circuit breaker. Coil 62 is formed about a coil form 66 of insulation, and the successive turns of the braid are separated from each other by insulation on the braid itself or by ribs 68 on coil form 66. The coil form fits tightly on core 70 of magnetic material which may be riveted to contact-carrier portion 60 or may be made integral therewith as shown. The axial length of core 70 is slightly less than that of the coil form 66 so that there is no danger of electrical contact being made between bimetal 50 and core 70. Contact carrier 20 is formed of magnetic material such as sheet iron, and has a portion 72 extending perpendicularly to the plane of the drawing (FIGS. 1 and 2), so that a magnetic circuit is formed including core 70, and contact-arm portions 60 and 72 that is closely coupled to bimetal 50. The bimetal is of magnetic material, and acts as an armature attracted toward coil 62 when the latter is energized. A suppleprojection or stop 58.

.biased counterclockwise by spring 36. Contact carrier 20 has an integral ear 74 which presses downward against an extension 76 of the tripping point compensating bimetal 54 (FIG. 5). Extension 76 extends laterally through an aperture 78 in the contact carrier 20. Spring .36 drives contact carrier 20 and contact element 42-50- 54 as a unit until the main bimetal 50 strikes the casing This stop limits the counterclockwise movement of the contact carrier about its pivot 22 and also provides counterclockwise bias for unit 42- 50-54 about pivot rivet 38. This insures engagement of the pivoted unit 42-50-54 with the ear 74 of the carrier 20, and locates the right hand of the main bimetal 50 for latchingengagement with the lower end 51 of the actuator 32.

In order to close the circuit breaker, operating handle 24 is moved counterclockwise about its pivot to apply thrust to link 34 and in that Way to bias the actuator 32 clockwise, into latched engagement with the bimetal 50 while the bimetal still rests on stop 58 of the casing wall 12. Further operating effort applied to the handle drives the contact carrier .20, actuator 32, bimetals 50-54, and

contact element 42 clockwise as a unit about the pivot 22.

Handle 24 and link 34 constitute two links of an operating toggle. When this toggle approaches its fully extended condition, contacts 44 and 46 engage. Further effort applied to handle 24 builds up contact pressure, forcing pivot spring 22 to flex downward and thus building up contact pressure. The operating toggle moves somewhat 'overcenter and locks the circuit breaker mechanism with the contacts closed when the projecting portion 26 of the handle reaches the left-hand or closed extremity of its stroke permitted by the casing. During the contact-closing operation of the mechanism, bimetal 50 lifts away and the upper surface of contact 44 is upwardly convex.

The plane that'is tangent to the point of engagement between contact portions 46, and 44 coincides with the face of the contact 46 in the construction shown. This plane is perpendicular to the plane that contains both the axis of pivot 38 and the point of contact engagement. Because of the right-angle relationship between these planes, the pressure at the contacts develops neither clockwise nor counterclockwise torque of the contact element 42 about pivot 38. By like token, endwise pressure of actuator 32 against bimetal 50 is arranged to provide direct thrust along the length of the bimetal through the axis of pivot 38. Because of this arrangement thrust along bimetal 50 does not produce any torque that biases bimetal 50 counterclockwise (which would tend to hold it in the latched configuration shown), nor does actuator v32 produce any clockwise torque that might tend to deflect bimetal 50 in the releasing direction. The mechanism in its closed condition as illustrated in FIG. 2 is thus stable mechanically. The configuration described results in little or no force acting on the movable-contact-latch structure 42-50-54 tending to hold it latched against clockwise movement about the pivot 38 in response to a. magnetic deflecting force or against the deflection of the unit. The only significant force acting on unit 42-50-54 tending to hold it latched against clockwise movement about pivot 38 in response to a magnietic deflecting force is the latch friction at the latched end of the bimetal. If added force were desired to hold the bimetal latched against the magnetic tripping force that would develop under short-circuit conditions, this may be arranged by changing the angle of the plane containing bimetal 50 relative to the plane containing both the axis of pivot 38 and the line or point of engagement of contacts 44 and 46.

Current through the circuit breaker flows from terminal 16 through contacts 44 and 46, through contact element 42 and bimetal 50, through coil 62 and flexible lead 64 to terminal 18. In the event of a moderate current excess, bimetal 50 heats gradually. The left-hand end of the bimetal 50 is fixed in position by the pivot 38 and the reaction of compensating bimetal 54 against the ear 74 on the carrier 20. Heating of the main bimetal 50 causes it to deflect downward until its right-hand end is clear of the end 51 of actuator 26. When this occurs, springs 22 and 36 are free to restore the parts to the configuration in FIGS. 1 and 4. Under conditions of sudden current rise of short-circuit proportions, element 50, 42 pivots clockwise as a unit toward magnetic core 70 and coil 62.

Under moderate-current conditions, a reaction point for the main bimetal 50 is provided adjacent the contact element 42, where bimetal 54 engages ear 74. This reaction point may be considered fixed. Correspondingly the left-hand end of bimetal 50 may be considered fixed with respect to the contact carrier 20. The end of the bimetal 50 engaged by the actuator 32 may be considered free. However, when local heating as by contact resistance or by an increase in ambient temperature causes the bimetal 50 to flex or curve in the tripping direction, the compensating bimetal 54 curves or flexes in the opposite direction and allows the fixed end of the bimetal 50 to move counterclockwise about its pivot 38. The compensator 54 acts as a reaction point 'or fulcrum for bimetal 50. The bimetal 50 is otherwise only held at its ends and would be free to curve upwardly at its center without releasing the actuator. The displacement of the reaction point, due to local heating or a rise in the ambient temperature of the compensator, has the eflect of cancelling all (or at least a substantial part) of what otherwise would be a movement of the free end of the main bimetal 50 in the tripping direction. The compensator thus reduces or eliminates the eflect of the ambient temperature and local heating on the bimetal 50. As a design consideration, less than 100% compensation is often considered desirable.

It will be recognized that both the main bimetal and the compensating bimetal 54 are located close to the contacts. Local heating at the contacts that may develop due to wear of the contacts (with resulting increased contact resistance) tends to add to the heating of the main bimetal normally caused by current flow in the bimetal, and this could cause a large deflection even though the current is moderate. However, the same local heating also causes reverse deflection of the compensating bimetal. This arrangement is thus particularly eflective in reducing nuisance tripping which has heretofore been a problem.

For calibrating purposes the contact carrier 20 includes a slot and the previously described car 74. When the circuit breaker is closed as in FIG. 2, a taper pin may be driven progressively into the aperture 78 driving the ear 74 downward thereby gradually reducing the gap between the bimetal 50 and the magnetic curcuit 60-70- 72. Momentary bursts of current of magnetic-tripping level can be passed through the coil at intervals, while maintaining normal latch pressure. When the gap is reduced to the proper size by this adjustment, the latch will trip. Subsequently, the latch is engaged again and current of the proper thermal calibration level is passed through it for the required time interval. A taper pin is driven into slot 80 to thereby spread the edges of that slot and thereby decrease the amount of overlap of actuator 32 across the end of bimetal 50 until release oc curs at this calibration level. Ear 74 and slot 80 thus provide independent magnetic and thermal overload-release adjustments. These adjustments are effected at a time prior to the assembly of the parts of FIG. 2 in an insulating housing, using an appropriate fixture for this purpose. Thereafter, when the circuit breaker is assembled into its housing, no further calibrating operations are needed.

Another embodiment of certain aspects of the invention is illustrated in FIG. 6. Tripping point compensator 54 is secured to the contact carrier 20 by an ear 82 which clamps 'one end of the compensating bimetal 54 between the ear and a projection 84 on the carrier 20'. The free end of the compensator 54 bears against a shoulder 55 on the movable contact-latch structure 42'- 50'. The free end of the compensator 54' acts as a stop limiting the counter-clockwise movement of the contact unit 42'-50' about the pivot 38 in the closed circuit position. The compensator 54' functions as described before in compensating for the effects of ambient temperature changes that affect the main bimetal. However, in this embodiment the free end of the compensative bimetal only touches the part 42 and is not in good heattransfer relationship thereto. It will be recalled that part 42' is the element that is heated by contact-resistance when current flows through contacts 44' and 46'. The fixed end of the compensating bimetal is relatively far from part 42'. The temperature of that fixed end is by far the most significant factor in determining the total bimetal deflection. Consequently compensator 54' can produce only a second-order effect in compensating for that component of main-bimetal deflection which is due to contact-resistance heating.

The compensating bimetals 54 and 54' are highly effec tive in compensating for the effects of ambient temperature changes and thus reducing nuisance tripping of the circuit breaker which is attributable to ambient temperature effects. The embodiment of FIGS. 1-5 additionally compensates for heating of bimetal 50 by heat conduction from contact element 42, and thus compensates for the direct heating of bimetal 50 that results from changes in contact resistance due to contact wear after repeated operations.

The foregoing specific embodiments of the invention are presently preferred, but it will be apparent that features of the invention may be utilized in different applications and in modified forms. Therefore the invention should be broadly construed in accordance with its full spirit and scope.

What I claim is:

1. A circuit breaker including a movable contact and a companion contact, a contact carrier for said movable contact movable between open and closed circuit positions, operating means for said carrier including a releasable member, and an overcurrent responsive bimetal latch cooperating with said releasable member when said contacts are closed, said bimetal latch and said movable contact comprising a latch unit having a mounting pivot on said carrier for releasing said releasable member to effect movement of said movable contact to said open position, said bimetal being arranged to deflect about said mounting pivot in response to thermal changes, and thermally responsive means extending between said latch unit and said carrier and providing a reaction point for said latch unit, said thermally responsive means including a compensating bimetal arranged to accommodate movement of said latch unit about said mounting pivot in response to common temperature changes affecting both said bimetals.

2. A circuit breaker according to claim 1 wherein the compensating bimetal compensator is secured to said latch unit and reacts against said carrier at the other.

3. A circuit breaker according to claim 1 wherein the compensating bimetal compensator is secured to said carrier and engages said latch unit.

4. A circuit breaker including a pivoted contact carrier, an actuator pivoted to the carrier, a combined contact-and-latch structure pivoted to said carrier and including a movable contact and an overcurrent latch cooperable with said actuator and a temperature responsive compensator element, a companion contact engageable by said movable contact, an opening spring acting on said carrier for driving the carrier and the movable contact therewith in the contact opening direction, said compensator element cooperating with a stop formed on said carrier for initially positioning said latch with respect to said actuator and for thereafter constituting a thermally varying reaction point for said actuator for providing thermal compensation.

5. A circuit breaker including a pivoted contact carrier, an actuator pivoted to the carrier, a combined contact-and-latch structure pivoted to said carrier and including a movable contact and a thermal overcurrent latch cooperable with said actuator, a companion contact engageable by said movable contact, an opening spring acting on said carrier for driving the carrier and the movable contact therewith in the contact opening direction, a temperature responsive compensator element, said compensator element acting between said carrier and said combined contact-and-latch structure so as to initially position said contact-and-latch with respect to said actuator and thereafter compensate for the effects of ambient temperature variations on said thermal latch.

6. A circuit breaker including a pivoted contact carrier, an actuator pivoted to the carrier, a combined contact-and-latch structure pivoted to said carrier and including a movable contact and a thermal overcurrent latch cooperable with said actuator, a companion contact engageable by said movable contact, an opening spring acting on said carrier for driving the carrier and the movable contact therewith in the contact opening direction, a temperature responsive compensator element mounted on said carrier and mechanically engaging said contactand latch structure compensator element so as to initially position said latch with respect to said actuator and to thereafter compensate for the effects of ambient temperature on said thermal latch.

7. A circuit breaker including an enclosing casing of insulation, a movable contact and a companion contact, an elongated carrier for said movable contact, a pivot in the casing supporting said contact-carrier between the ends thereof, an actuator pivoted to one end of the contact-carrier, overload release means including a current responsive bimetal normally latching said actuator when the circuit breaker is closed, a driving toggle articulated to said actuator and including an operating handle for driving and locking the contact-carrier closed, and an opening spring biasing said contact-carrier open, said movable contact and said bimetal being united and being pivoted as a unit to said carrier, said unit being further provided with a temperature responsive element mounted adjacent said bimetal, said temperature responsive element providing mechanical coupling between said overload release means and said carrier, said temperature responsive element disposing said latch in the path of said actuator initially and adjusting the spatial relationship between said latch and said actuator according to the ambient temperature.

8. A circuit breaker including an enclosing casing of insulation, a movable contact and a companion contact, an elongated carrier for said movable contact, a pivot in the casing supporting said contact-carrier between the ends thereof, an actuator pivoted to one end of the contact-carrier, overload release means including a latch normally latching said actuator when the circuit breaker is closed, a driving toggle articulated to said actuator and including an operating handle for driving and locking the contact-carrier closed, and an opening springv biasing said contact-carrier open, said movable contact and said latch being united and being pivoted as a unit to said carrier, said unit being further provided with. a temperature responsive element secured to said contactlatch unit, said carrier having a stop engaged by said temperature responsive element for disposing said latch in the path of said actuator initially and for adjusting the spatial relationship between said latch and said actuator according to the ambient temperature.

References Cited by the Examiner UNITED STATES PATENTS Sachs 200-416 Fisher 200-1 16 Cole 2001 16 Jackson 200-116 Christensen 200-1 16 Marquis 200-116 10 BERNARD A. GILHEANY, Primary Examiner. 

1. A CIRCUIT BREAKER INCLUDING A MOVABLE CONTACT AND A COMPANION CONTACT, A CONTACT CARRIER FOR SAID MOVABLE CONTACT MOVABLE BETWEEN "OPEN" AND "CLOSED" CLOSED CIRCUIT POSITIONS, OPERATING MEANS FOR SAID CARRIER INCLUDING A RELEASABLE MEMBER, AND AN OVERCURRENT RESPONSIVE BIMETAL LATCH COOPERATING WITH SAID RELEASABLE MEMBER WHEN SAID CONTACTS ARE CLOSED, SAID BIMETAL LATCH AND SAID MOVABLE CONTACT COMPRISING A LATCH UNIT HAVING A MOUNTING PIVOT ON SAID CARRIER FOR RELEASING SAID RELEASABLE MEMBER TO EFFECT MOVEMENT OF SAID MOVABLE CONTACT TO SAID "OPEN" POSITION, SAID BIMETAL BEING ARRANGED TO DEFLECT ABOUT SAID MOUNTING PIVOT IN RESPONSE TO THERMAL CHANGES, AND THERMALLY RESPONSIVE MEANS EXTENDING BETWEEN SAID LATCH UNIT AND SAID CARRIER AND PROVIDING A REACTION POINT FOR SAID LATCH UNIT, SAID THERMALLY RESPONSIVE MEANS INCLUDING A COMPENSATING BIMETAL ARRANGED TO ACCOMMODATE MOVEMENT OF SAID LATCH UNIT ABOUT SAID MOUNTING PIVOT IN RESPONSE TO COMMON TEMPERATURE CHANGES AFFECTING BOTH SAID BIMETALS. 